Facilitated processing for controlling bonding between sheet and carrier

ABSTRACT

A method of forming an article from a glass sheet ( 20 ) having a glass-sheet bonding surface ( 24 ) and a glass carrier ( 10 ) having a carrier bonding surface ( 14 ). At least one of the glass sheet and carrier bonding surfaces is coated with a surface modification layer ( 30 ), and then the glass sheet is connected with the carrier via the surface modification layer. From the perimeter of the glass sheet and the carrier while connected, there is removed a portion of the surface modification layer so as to expose a portion ( 19, 29 ) of the bonding surface on each of the glass sheet and the carrier. The glass sheet and carrier are then heated at a temperature ≧400° C. so as to bond the perimeter of the glass sheet ( 26 ) with the perimeter of the carrier ( 16 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 365 ofInternational Patent Application Serial No. PCT/US13/74859 filed on Dec.13, 2013 designating the United States of America, which claims thebenefit of priority under 35 U.S.C. § 119 of U.S. ProvisionalApplication Ser. No. 61/736,880, filed on Dec. 13, 2012, the content ofeach of which is relied upon and incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

The present invention is directed to articles having flexible sheets oncarriers and, more particularly to articles and methods enablingfacilitated assembly of flexible glass sheets onto glass carriers.

TECHNICAL BACKGROUND

Flexible substrates offer the promise of cheaper devices usingroll-to-roll processing, and the potential to make thinner, lighter,more flexible and durable displays. However, the technology, equipment,and processes required for roll-to-roll processing of high qualitydisplays are not yet fully developed. Since panel makers have alreadyheavily invested in toolsets to process large sheets of glass,laminating a flexible substrate to a carrier and making display devicesby a sheet-to-sheet processing offers a shorter term solution to developthe value proposition of thinner, lighter, and more flexible displays.Displays have been demonstrated on polymer sheets for examplepolyethylene naphthalate (PEN) where the device fabrication was sheet tosheet with the PEN laminated to a glass carrier. The upper temperaturelimit of the PEN limits the device quality and process that can be used.In addition, the high permeability of the polymer substrate leads toenvironmental degradation of OLED devices where a near hermetic packageis required. Thin film encapsulation offers the promise to overcome thislimitation, but it has not yet been demonstrated to offer acceptableyields at large volumes.

In a similar manner, display devices can be manufactured using a glasscarrier laminated to one or more thin glass substrates. It isanticipated that the low permeability and improved temperature andchemical resistance of the thin glass will enable higher performancelonger lifetime flexible displays.

However, the thermal, vacuum, solvent and acidic, and ultrasonic, FlatPanel Display (FPD) processes require a robust bond for thin glass boundto a carrier. FPD processes typically involve vacuum deposition(sputtering metals, transparent conductive oxides and oxidesemiconductors, Chemical Vapor Deposition (CVD) deposition of amorphoussilicon, silicon nitride, and silicon dioxide, and dry etching of metalsand insulators), thermal processes (including ˜300-400° C. CVDdeposition, up to 600° C. p-Si crystallization, 350-450° C. oxidesemiconductor annealing, up to 650° C. dopant annealing, and ˜200-350°C. contact annealing), acidic etching (metal etch, oxide semiconductoretch), solvent exposure (stripping photoresist, deposition of polymerencapsulation), and ultrasonic exposure (in solvent stripping ofphotoresist and aqueous cleaning, typically in alkaline solutions).

Adhesive wafer bonding has been widely used in Micromechanical Systems(MEMS) and semiconductor processing for back end steps where processesare less harsh. Commercial adhesives by Brewer Science and Henkel aretypically thick polymer adhesive layers, 5-200 microns thick. The largethickness of these layers creates the potential for large amounts ofvolatiles, trapped solvents, and adsorbed species to contaminate FPDprocesses. These materials thermally decompose and outgas above ˜250° C.The materials also may cause contamination in downstream steps by actingas a sink for gases, solvents and acids which can outgas in subsequentprocesses.

U.S. Provisional Application Ser. No. 61/596,727 filed on Feb. 8, 2012,entitled Processing Flexible Glass with a Carrier (hereinafter US '727)discloses that the concepts therein involve bonding a thin sheet, forexample, a flexible glass sheet, to a carrier initially by van der Waalsforces, then increasing the bond strength in certain regions whileretaining the ability to remove portions of the thin sheet afterprocessing the thin sheet/carrier to form devices (for example,electronic or display devices, components of electronic or displaydevices, organic light emitting device (OLED) materials, photo-voltaic(PV) structures, or thin film transistors), thereon. At least a portionof the thin glass is bonded to a carrier such that there is preventeddevice process fluids from entering between the thin sheet and carrier,whereby there is reduced the chance of contaminating downstreamprocesses, i.e., the bonded seal portion between the thin sheet andcarrier is hermetic, and in some preferred embodiments, this sealencompasses the outside of the article thereby preventing liquid or gasintrusion into or out of any region of the sealed article.

US '727 goes on to disclose that in low temperature polysilicon (LTPS)(low temperature compared to solid phase crystallization processingwhich can be up to about 750° C.) device fabrication processes,temperatures approaching 600° C. or greater, vacuum, and wet etchenvironments may be used. These conditions limit the materials that maybe used, and place high demands on the carrier/thin sheet. Accordingly,what is desired is a carrier approach that utilizes the existing capitalinfrastructure of the manufacturers, enables processing of thin glass,i.e., glass having a thickness ≦0.3 mm thick, without contamination orloss of bond strength between the thin glass and carrier at higherprocessing temperatures, and wherein the thin glass de-bonds easily fromthe carrier at the end of the process.

One commercial advantage to the approach disclosed in US '727 is that,as noted in US '727, manufacturers will be able to utilize theirexisting capital investment in processing equipment while gaining theadvantages of the thin glass sheets for PV, OLED, LCDs and patternedThin Film Transistor (TFT) electronics, for example. Additionally, thatapproach enables process flexibility, including: that for cleaning andsurface preparation of the thin glass sheet and carrier to facilitatebonding; that for strengthening the bond between the thin sheet andcarrier at the bonded area; that for maintaining releasability of thethin sheet from the carrier at the non-bonded (or reduced/low-strengthbond) area; and that for cutting the thin sheets to facilitateextraction from the carrier.

In the glass-to-glass bonding process, the glass surfaces are cleaned toremove all metal, organic and particulate residues, and to leave amostly silanol terminated surface. The glass surfaces are first broughtinto intimate contact where van der Waals and/or Hydrogen-bonding forcespull them together. With heat and optionally pressure, the surfacesilanol groups condense to form strong covalent Si—O—Si bonds across theinterface, permanently fusing the glass pieces. Metal, organic andparticulate residue will prevent bonding by obscuring the surfacepreventing the intimate contact required for bonding. A high silanolsurface concentration is also required to form a strong bond as thenumber of bonds per unit area will be determined by the probability oftwo silanol species on opposing surfaces reacting to condense out water.Zhuravlel has reported the average number of hydroxyls per nm² for wellhydrated silica as 4.6 to 4.9. Zhuravlel, L. T., The Surface Chemistryof Amorphous Silika, Zhuravlev Model, Colloids and Surfaces A:Physiochemical Engineering Aspects 173 (2000) 1-38. In US '727, anon-bonding region is formed within a bonded periphery, and the primarymanner described for forming such non-bonding area is increasing surfaceroughness. An average surface roughness of greater than 2 nm Ra canprevent glass to glass bonds forming during the elevated temperature ofthe bonding process.

SUMMARY

There is a need for a facilitated manner of assembling a thinsheet—carrier article that can withstand the rigors of the FPDprocessing, including high temperature processing (without outgassingthat would be incompatible with the semiconductor or display makingprocesses in which it will be used), yet allow sections of the thinsheet to be removed from the carrier. The present specificationdescribes ways to control the adhesion between the carrier and thinsheet to create a temporary bond sufficiently strong to survive FPDprocessing (including LTPS processing) but weak enough to permitdebonding of portions of the sheet from the carrier, even afterhigh-temperature processing. Such controlled bonding can be utilized tocreate an article having patterned areas of controlled bonding andcovalent bonding between a carrier and a sheet. More specifically, thepresent disclosure provides surface modification layers (includingvarious materials and associated surface heat treatments), that may beprovided on the thin sheet, the carrier, or both, to control bothroom-temperature van der Waals, and/or hydrogen, bonding and hightemperature covalent bonding between portions of the thin sheet andcarrier. Even more specifically, the room-temperature bonding may becontrolled so as to be sufficient to hold the thin sheet and carriertogether during vacuum processing, wet processing, and/or ultrasoniccleaning processing. And at the same time, the high temperature covalentbonding may be controlled so as to prevent a permanent bond betweenportions of the thin sheet and carrier during high temperatureprocessing, as well as maintain a sufficient bond to preventdelamination during high temperature processing. In alternativeembodiments, the surface modification layers may be used to createvarious controlled bonding areas (wherein the carrier and sheet remainsufficiently bonded through various processes, including vacuumprocessing, wet processing, and/or ultrasonic cleaning processing),together with covalent bonding regions to provide for further processingoptions, for example, maintaining hermeticity between the carrier andsheet even after dicing the article into smaller pieces for additionaldevice processing. Still further, some surface modification layersprovide control of the bonding between the carrier and sheet while, atthe same time, reduce outgassing emissions during the harsh conditionsin an FPD (for example LTPS) processing environment, including hightemperature and/or vacuum processing, for example.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing thevarious aspects as exemplified in the written description and theappended drawings. It is to be understood that both the foregoinggeneral description and the following detailed description are merelyexemplary of the various aspects, and are intended to provide anoverview or framework to understanding the nature and character of theinvention as it is claimed.

The accompanying drawings are included to provide a furtherunderstanding of principles of the invention, and are incorporated inand constitute a part of this specification. The drawings illustrate oneor more embodiment(s), and together with the description serve toexplain, by way of example, principles and operation of the invention.It is to be understood that various features disclosed in thisspecification and in the drawings can be used in any and allcombinations. By way of non-limiting example the various features may becombined with one another as set forth in the appended claims

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of an article having carrier bonded to athin sheet with a surface modification layer therebetween.

FIG. 2 is an exploded and partially cut-away view of the article in FIG.1.

FIG. 3 is a graph of surface hydroxyl concentration on silica as afunction of temperature.

FIG. 4 is a graph of the surface energy of an SC1-cleaned sheet of glassas a function annealing temperature.

FIG. 5 is a graph of the surface energy of a thin fluoropolymer filmdeposited on a sheet of glass as a function of the percentage of one ofthe constituent materials from which the film was made.

FIG. 6 is a schematic top view of a thin sheet bonded to a carrier bybonding areas.

FIG. 7 is a schematic top view of a sheet and carrier.

FIG. 8 is a cross-sectional view as taken along line 8-8 in FIG. 7 afterthe sheet and carrier have been connected via a surface modificationlayer.

FIG. 9 is a cross-sectional view as taken along line 8-8 in FIG. 7 afterthe surface modification layer has been partially removed.

FIG. 10 is a cross-sectional view as taken along line 8-8 in FIG. 7after the carrier and sheet have been bonded in the bonding region.

FIG. 11 is a schematic top view of a sheet and a carrier havingpatterned bonding areas.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation andnot limitation, example embodiments disclosing specific details are setforth to provide a thorough understanding of various principles of thepresent invention. However, it will be apparent to one having ordinaryskill in the art, having had the benefit of the present disclosure, thatthe present invention may be practiced in other embodiments that departfrom the specific details disclosed herein. Moreover, descriptions ofwell-known devices, methods and materials may be omitted so as not toobscure the description of various principles of the present invention.Finally, wherever applicable, like reference numerals refer to likeelements.

Ranges can be expressed herein as from “about” one particular value,and/or to “about” another particular value. When such a range isexpressed, another embodiment includes from the one particular valueand/or to the other particular value. Similarly, when values areexpressed as approximations, by use of the antecedent “about,” it willbe understood that the particular value forms another embodiment. Itwill be further understood that the endpoints of each of the ranges aresignificant both in relation to the other endpoint, and independently ofthe other endpoint.

Directional terms as used herein—for example up, down, right, left,front, back, top, bottom—are made only with reference to the figures asdrawn and are not intended to imply absolute orientation.

As used herein, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. Thus, forexample, reference to a “component” includes aspects having two or moresuch components, unless the context clearly indicates otherwise.

In US '727 there are provided solutions for allowing the processing of athin glass sheet on a carrier, whereby at least portions of the thinglass sheet remain “non-bonded” so that devices processed on the thinglass sheet may be removed from the carrier. However, the periphery ofthe thin glass is permanently (or covalently, or hermetically) bonded tothe carrier glass through the formation of covalent Si—O—Si bonds. Thiscovalently bonded perimeter hermetically seals the carrier with the thinglass in this permanently bonded zone so that process fluids cannotenter between the thin sheet and carrier.

The present disclosure sets forth articles and methods for facilitatingthe formation of a hermetic bond between the thin sheet and carrier soas to enable a thin sheet to be processed through the harsh environmentof the FPD processing lines, including high temperatureprocessing—wherein high temperature processing is processing at atemperature ≧400° C., and may vary depending upon the type of devicebeing made, for example, temperatures up to about 450° C. as inamorphous silicon or amorphous indium gallium zinc oxide (IGZO)backplane processing, up to about 500-550° C. as in crystalline IGZOprocessing, or up to about 600-650° C. as is typical in LTPS processes.

As shown in FIGS. 1 and 2, a glass article 2 has a thickness 8, andincludes a carrier 10 having a thickness 18, a thin sheet 20 (i.e., onehaving a thickness of ≦300 microns, including but not limited tothicknesses of, for example, 10-50 microns, 50-100 microns, 100-150microns, 150-300 microns, 300, 250, 200 190, 180, 170, 160, 150 140,130, 120 110 100, 90, 80, 70, 60, 50, 40 30, 20, or 10, microns) havinga thickness 28, and a surface modification layer 30 having a thickness38. The glass article 2 is designed to allow the processing of thinsheet 20 in equipment designed for thicker sheets (i.e., those on theorder of ≧0.4 mm, e.g., 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm,or 1.0 mm) although the thin sheet 20 itself is ≦300 microns. That is,the thickness 8, which is the sum of thicknesses 18, 28, and 38, isdesigned to be equivalent to that of the thicker sheet for which a pieceof equipment—for example, equipment designed to dispose electronicdevice components onto substrate sheets—was designed to process. Forexample, if the processing equipment was designed for a 700 micronsheet, and the thin sheet had a thickness 28 of 300 microns, thenthickness 18 would be selected as 400 microns, assuming that thickness38 is negligible. That is, the surface modification layer 30 is notshown to scale; instead, it is greatly exaggerated for sake ofillustration only. Additionally, the surface modification layer is shownin cut-away. In actuality, the surface modification layer would bedisposed uniformly over the bonding surface 14 when providing a reusablecarrier. Typically, thickness 38 will be on the order of nanometers, forexample 0.1 to 2.0, or up to 10 nm, and in some instances may be up to100 nm. The thickness 38 may be measured by ellipsometer. Additionally,the presence of a surface modification layer may be detected by surfacechemistry analysis, for example by ToF Sims mass spectrometry.Accordingly, the contribution of thickness 38 to the article thickness 8is negligible and may be ignored in the calculation for determining asuitable thickness 18 of carrier 10 for processing a given thin sheet 20having a thickness 28. However, to the extent that surface modificationlayer 30 has any significant thickness 38, such may be accounted for indetermining the thickness 18 of a carrier 10 for a given thickness 28 ofthin sheet 20, and a given thickness for which the processing equipmentwas designed.

Carrier 10 has a first surface 12, a bonding surface 14, a perimeter 16,and thickness 18. Further, the carrier 10 may be of any suitablematerial including glass, for example. The carrier need not be glass,but instead can be ceramic, glass-ceramic, or metal (as the surfaceenergy and/or bonding may be controlled in a manner similar to thatdescribed below in connection with a glass carrier). If made of glass,carrier 10 may be of any suitable composition includingalumino-silicate, boro-silicate, alumino-boro-silicate,soda-lime-silicate, and may be either alkali containing or alkali-freedepending upon its ultimate application. Thickness 18 may be from about0.2 to 3 mm, or greater, for example 0.2, 0.3, 0.4, 0.5, 0.6, 0.65, 0.7,1.0, 2.0, or 3 mm, or greater, and will depend upon the thickness 28,and thickness 38 when such is non-negligible, as noted above.Additionally, the carrier 10 may be made of one layer, as shown, ormultiple layers (including multiple thin sheets) that are bondedtogether. Further, the carrier may be of a Gen 1 size or larger, forexample, Gen 2, Gen 3, Gen 4, Gen 5, Gen 8 or larger (e.g., sheet sizesfrom 100 mm×100 mm to 3 meters×3 meters or greater).

The thin sheet 20 has a first surface 22, a bonding surface 24, aperimeter 26, and thickness 28. Perimeters 16 and 26 may be of anysuitable shape, may be the same as one another, or may be different fromone another. Further, the thin sheet 20 may be of any suitable materialincluding glass, ceramic, or glass-ceramic, for example. When made ofglass, thin sheet 20 may be of any suitable composition, includingalumino-silicate, boro-silicate, alumino-boro-silicate,soda-lime-silicate, and may be either alkali containing or alkali freedepending upon its ultimate application. The coefficient of thermalexpansion of the thin sheet could be matched relatively closely withthat of the carrier to prevent warping of the article during processingat elevated temperatures. The thickness 28 of the thin sheet 20 is 300microns or less, as noted above. Further, the thin sheet may be of a Gen1 size or larger, for example, Gen 2, Gen 3, Gen 4, Gen 5, Gen 8 orlarger (e.g., sheet sizes from 100 mm×100 mm to 3 meters×3 meters orgreater).

Not only does the article 2 need to have the correct thickness to beprocessed in the existing equipment, it will also need to be able tosurvive the harsh environment in which the processing takes place. Forexample, flat panel display (FPD) processing may include wet ultrasonic,vacuum, and high temperature (e.g., ≧400° C.), processing. For someprocesses, as noted above, the temperature may be ≧500° C., or ≧600° C.,and up to 650° C.

In order to survive the harsh environment in which article 2 will beprocessed, as during FPD manufacture for example, the bonding surface 14should be bonded to bonding surface 24 with sufficient strength so thatthe thin sheet 20 does not separate from carrier 10. And this strengthshould be maintained through the processing so that the thin sheet 20does not separate from the carrier 10 during processing. Further, toallow portions of the thin sheet 20 to be removed from carrier 10, thebonding surface 14 should not be bonded to bonding surface 24 toostrongly either by the initially designed bonding force, and/or by abonding force that results from a modification of the initially designedbonding force as may occur, for example, when the article undergoesprocessing at high temperatures, e.g., temperatures of ≧400° C. Thesurface modification layer 30 may be used to control the strength ofbonding between bonding surface 14 and bonding surface 24 so as to thisobjective. The controlled bonding force is achieved by controlling thecontributions of van der Waals (and/or hydrogen bonding) and covalentattractive energies to the total adhesion energy which is controlled bymodulating the polar and non-polar surface energy components of the thinsheet 20 and the carrier 10. This controlled bonding is strong enough tosurvive FPD processing (including wet, ultrasonic, vacuum, and thermalprocesses including temperatures ≧400° C., and in some instances,processing temperatures of ≧500° C., or ≧600° C., and up to 650° C.) andremain de-bondable by application of sufficient separation force and yetby a force that will not cause catastrophic damage (e.g., the breakingor cracking into two or more pieces) to the thin sheet 20 and/or thecarrier 10. Such de-bonding permits removal of portions of the thinsheet 20 and the devices fabricated thereon.

Although the surface modification layer 30 is shown as a solid layerbetween thin sheet 20 and carrier 10, such need not be the case. Forexample, the layer 30 may be on the order of 0.1 to 2 nm thick, and maynot completely cover every bit of the bonding surface 14. For example,the coverage may be ≦100%, from 1% to 100%, from 10% to 100%, from 20%to 90%, or from 50% to 90%. In other embodiments, the layer 30 may be upto 10 nm thick, or in other embodiments even up to 100 nm thick. Thesurface modification layer 30 may be considered to be disposed betweenthe carrier 10 and thin sheet 20 even though it may not contact one orthe other of the carrier 10 and thin sheet 20. In any event, animportant aspect of the surface modification layer 30 is that itmodifies the ability of the bonding surface 14 to bond with bondingsurface 24, thereby controlling the strength of the bond between thecarrier 10 and the thin sheet 20. The material and thickness of thesurface modification layer 30, as well as the treatment of the bondingsurfaces 14, 24 prior to bonding, can be used to control the strength ofthe bond (energy of adhesion) between carrier 10 and thin sheet 20.

In general, the energy of adhesion between two surfaces is given by (“Atheory for the estimation of surface and interfacial energies. I.derivation and application to interfacial tension”, L. A. Girifalco andR. J. Good, J. Phys. Chem., V 61, p 904):W=γ ₁+γ₂−γ₁₂  (1)where γ₁, γ₂ and γ₁₂ are the surface energies of surface 1, surface 2and the interfacial energy of surface 1 and 2 respectively. Theindividual surface energies are usually a combination of two terms; adispersion component γ^(d), and a polar component γ^(p)γ=γ^(d)+γ^(p)  (2)

When the adhesion is mostly due to London dispersion forces (γ^(d)) andpolar forces for example hydrogen bonding (γ^(p)), the interfacialenergy could be given by (Girifalco and R. J. Good, as mentioned above):γ₁₂=γ₁+γ₂−2√{square root over (γ₁ ^(d)γ₂ ^(d))}−2√{square root over (γ₁^(p)γ₂ ^(p))}  (3)

After substituting (3) in (1), the energy of adhesion could beapproximately calculated as:W˜2[√{square root over (γ₁ ^(d)γ₂ ^(d))}+√{square root over (γ₁ ^(p)γ₂^(p))}]  (4)

In the above equation (4), only van der Waal (and/or hydrogen bonding)components of adhesion energies are considered. These includepolar-polar interaction (Keesom), polar-non polar interaction (Debye)and nonpolar-nonpolar interaction (London). However, other attractiveenergies may also be present, for example covalent bonding andelectrostatic bonding. So, in a more generalized form, the aboveequation is written as:W˜2[√{square root over (γ₁ ^(d)γ₂ ^(d))}+√{square root over (γ₁ ^(p)γ₂^(p))}]+w _(c) +w _(e)  (4)where w_(c) and w_(e) are the covalent and electrostatic adhesionenergies. The covalent adhesion energy is rather common, as in siliconwafer bonding where an initially hydrogen bonded pair of wafers areheated to a higher temperature to convert much or all thesilanol-silanol hydrogen bonds to Si—O—Si covalent bonds. While theinitial, room temperature, hydrogen bonding produces an adhesion energyof the order of ˜100-200 mJ/m² which allows separation of the bondedsurfaces, a fully covalently bonded wafer pair as achieved during hightemperature processing (on the order of 400 to 800° C.) has adhesionenergy of ˜1000-3000 mJ/m² which does not allow separation of the bondedsurfaces; instead, the two wafers act as a monolith. On the other hand,if both the surfaces are perfectly coated with a low surface energymaterial, for example a fluoropolymer, with thickness large enough toshield the effect of the underlying substrate, the adhesion energy wouldbe that of the coating material, and would be very low leading to low orno adhesion between the bonding surfaces 14, 24, whereby the thin sheet20 would not be able to be processed on carrier 10. Consider two extremecases: (a) two standard clean 1 (SC1, as known in the art) cleaned glasssurfaces saturated with silanol groups bonded together at roomtemperature via hydrogen bonding (whereby the adhesion energy is˜100-200 mJ/m²) followed by heating to high temperature which convertsthe silanol groups to covalent Si—O—Si bonds (whereby the adhesionenergy becomes 1000-3000 mJ/m²). This latter adhesion energy is too highfor the pair of glass surfaces to be detachable; and (b) two glasssurfaces perfectly coated with a fluoropolymer with low surface adhesionenergy (˜12 mJ/m² per surface) bonded at room temperature and heated tohigh temperature. In this latter case (b), not only do the surfaces notbond (because the total adhesion energy of ˜24 mJ/m², when the surfacesare put together, is too low), they do not bond at high temperatureeither as there are no (or too few) polar reacting groups Between thesetwo extremes, a range of adhesion energies exist, for example between50-1000 mJ/m², which can produce the desired degree of controlledbonding. Accordingly, the inventors have found various manners ofproviding a surface modification layer 30 leading to an adhesion energythat is between these two extremes, and such that there can be produceda controlled bonding that is sufficient enough to maintain a pair ofglass substrates (for example a glass carrier 10 and a thin glass sheet20) bonded to one another through the rigors of FPD processing but alsoof a degree that (even after high temperature processing of, e.g. ≧400°C.) allows the detachment of portions of the thin sheet 20 from thecarrier 10 after processing is complete. Moreover, the detachment ofportions of the thin sheet 20 from the carrier 10 can be performed bymechanical forces, and in such a manner that there is no catastrophicdamage to at least the portions of the thin sheet 20, and preferablyalso so that there is no catastrophic damage to the carrier 10.

Equation (5) describes that the adhesion energy is a function of foursurface energy parameters plus the covalent and electrostatic energy, ifany.

An appropriate adhesion energy can be achieved by judicious choice ofsurface modifiers, i.e., of surface modification layer 30, and/orthermal treatment of the surfaces prior to bonding. The appropriateadhesion energy may be attained by the choice of chemical modifiers ofeither one or both of bonding surface 14 and bonding surface 24, whichin turn control both the van der Waal (and/or hydrogen bonding, as theseterms are used interchangeably throughout the specification) adhesionenergy as well as the likely covalent bonding adhesion energy resultingfrom high temperature processing (e.g., on the order of ≧400° C.). Forexample, taking a bonding surface of SC1 cleaned glass (that isinitially saturated with silanol groups with high polar component ofsurface energy), and coating it with a low energy fluoropolymer providesa control of the fractional coverage of the surface by polar andnon-polar groups. This not only offers control of the initial van derWaals (and/or hydrogen) bonding at room temperature, but also providescontrol of the extent/degree of covalent bonding at higher temperature.Control of the initial van der Waals (and/or hydrogen) bonding at roomtemperature is performed so as to provide a bond of one surface to theother to allow vacuum and or spin-rinse-dry (SRD) type processing, andin some instances also an easily formed bond of one surface to theother—wherein the easily formed bond can be performed at roomtemperature without application of externally applied forces over theentire area of the thin sheet 20 as is done in pressing the thin sheet20 to the carrier 10 with a squeegee, or with a reduced pressureenvironment. That is, the initial van der Waals bonding provides atleast a minimum degree of bonding holding the thin sheet and carriertogether so that they do not separate if one is held and the other isallowed to be subjected to the force of gravity. In most cases, theinitial van der Walls (and/or hydrogen) bonding will be of such anextent that the article may also go through vacuum, SRD, and ultrasonicprocessing without the thin sheet delaminating from the carrier. Thisprecise control of both van der Waal (and/or hydrogen bonding) andcovalent interactions at appropriate levels via surface modificationlayer 30 (including the materials from which it is made and/or thesurface treatment of the surface to which it is applied), and/or by heattreatment of the bonding surfaces prior to bonding them together,achieves the desired adhesion energy that allows thin sheet 20 to bondwith carrier 10 throughout FPD style processing, while at the same time,allowing portions of the thin sheet 20 to be separated (by anappropriate force avoiding damage to the thin sheet 20 and/or carrier)from the carrier 10 after FPD style processing. In addition, inappropriate circumstances, electrostatic charge could be applied to oneor both glass surfaces to provide another level of control of theadhesion energy.

FPD processing for example p-Si and oxide TFT fabrication typicallyinvolve thermal processes at temperatures above 400° C., above 500° C.,and in some instances at or above 600° C., up to 650° C. which wouldcause glass to glass bonding of a thin glass sheet 20 with a glasscarrier 10 in the absence of surface modification layer 30. Thereforecontrolling the formation of Si—O—Si bonding leads to a reusablecarrier. One method of controlling the formation of Si—O—Si bonding atelevated temperature is to reduce the concentration of surface hydroxylson the surfaces to be bonded.

As shown in FIG. 3, which is Iler's plot (R. K. Iller: The Chemistry ofSilica (Wiley-Interscience, New York, 1979) of surface hydroxylconcentration on silica as a function of temperature, the number ofhydroxyls (OH groups) per square nm decreases as the temperature of thesurface increases. Thus, heating a silica surface (and by analogy aglass surface, for example bonding surface 14 and/or bonding surface 24)reduces the concentration of surface hydroxyls, decreasing theprobability that hydroxyls on two glass surfaces will interact. Thisreduction of surface hydroxyl concentration in turn reduces the Si—O—Sibonds formed per unit area, lowering the adhesive force. However,eliminating surface hydroxyls requires long annealing times at hightemperatures (above 750° C. to completely eliminate surface hydroxyls).Such long annealing times and high annealing temperatures result in anexpensive process, and one which is not practical as it is likely to beabove the strain point of typical display glass.

From the above analysis, the inventors have found that an articleincluding a thin sheet and a carrier, suitable for FPD processing(including LTPS processing), can be made by balancing the followingthree concepts:

(1) Modification of the carrier and/or thin sheet bonding surface(s), bycontrolling initial room temperature bonding, which can be done bycontrolling van der Waals (and/or hydrogen) bonding, to create amoderate adhesion energy (for example, having a surface energy of >40mJ/m² per surface prior to the surfaces being bonded) to facilitateinitial room temperature bonding, and sufficient to survivenon-high-temperature FPD processes, for example, vacuum processing, SRDprocessing, and/or ultrasonic processing;

(2) Surface modification of a carrier and/or a thin sheet in a mannerthat is thermally stable to survive FPD processes without outgassingwhich can cause delamination and/or unacceptable contamination in thedevice fabrication, for example, contamination unacceptable to thesemiconductor and/or display making processes in which the article maybe used; and

(3) Controlling bonding at high temperatures, which can be done bycontrolling the carrier surface hydroxyl concentration, andconcentration of other species capable of forming strong covalent bondsat elevated temperatures (e.g., temperature ≧400° C.), whereby there canbe controlled the bonding energy between the bonding surfaces of thecarrier and the thin sheet such that even after high temperatureprocessing (especially through thermal processes in the range of500-650° C., as in FPD processes) the adhesive force between the carrierand thin sheet remains within a range that allows debonding of portionsof the thin sheet from the carrier with a separation force that does notdamage at least the thin sheet (and preferably that does not damageeither the thin sheet or the carrier), and yet sufficient enough tomaintain the bond between the carrier and thin sheet so that they do notdelaminate during processing.

Further, the inventors have found that the use of a surface modificationlayer 30, together with bonding surface preparation as appropriate, canbalance the above concepts so as readily to achieve a controlled bondingarea, that is, a bonding area that provides a sufficientroom-temperature bond between the thin sheet 20 and carrier 10 to allowthe article 2 to be processed in FPD type processes (including vacuumand wet processes), and yet one that controls covalent bonding betweenthe thin sheet 20 and carrier 10 (even at elevated temperatures ≧400°C.) so as to allow portions of the thin sheet 20 to be removed from thecarrier 10 (without damage to at least the thin sheet, and preferablywithout damage to the carrier also) after the article 2 has finishedhigh temperature processing, for example, FPD type processing or LTPSprocessing. To evaluate potential bonding surface preparations, andsurface modification layers, that would provide a reusable carriersuitable for FPD processing, a series of tests were used to evaluate thesuitability of each. Different FPD applications have differentrequirements, but LTPS and Oxide TFT processes appear to be the moststringent at this time and, thus, tests representative of steps in theseprocesses were chosen, as these are desired applications for the article2. Vacuum processes, wet cleaning (including SRD and ultrasonic typeprocesses) and wet etching are common to many FPD applications. TypicalaSi TFT fabrication requires processing up to 320° C. Annealing at 400°C. is used in oxide TFT processes, whereas crystallization and dopantactivation steps over 600° C. are used in LTPS processing. Accordingly,the following five tests were used to evaluate the likelihood that aparticular bonding surface preparation and surface modification layer 30would allow a thin sheet 20 to remain bonded to a carrier 10 throughoutFPD processing, while allowing the thin sheet 20 to be removed from thecarrier 10 (without damaging the thin sheet 20 and/or the carrier 10)after such processing (including processing at temperatures ≧400° C.).The tests were performed in order, and a sample progressed from one testto the next unless there was failure of the type that would not permitthe subsequent testing.

(1) Vacuum testing. Vacuum compatibility testing was performed in an STSMultiplex PECVD loadlock (available from SPTS, Newport, UK)—The loadlockwas pumped by an Ebara A10S dry pump with a soft pump valve (availablefrom Ebara Technologies Inc., Sacramento, Calif. A sample was placed inthe loadlock, and then the loadlock was pumped from atmospheric pressuredown to 70 mTorr in 45 sec. Failure, indicated by a notation of “F” inthe “Vacuum” column of the tables below, was deemed to have occurred ifthere was: (a) a loss of adhesion between the carrier and the thin sheet(by visual inspection with the naked eye, wherein failure was deemed tohave occurred if the thin sheet had fallen off of the carrier or waspartially debonded therefrom); (b) bubbling between the carrier and thethin sheet (as determined by visual inspection with the nakedeye—samples were photographed before and after the processing, and thencompared, failure was determined to have occurred if defects increasedin size by dimensions visible to the unaided eye); or (c) movement ofthe thin sheet relative to the carrier (as determined by visualobservation with the naked eye—samples were photographed before andafter testing, wherein failure was deemed to have occurred if there wasa movement of bond defects, e.g., bubbles, or if edges debonded, or ifthere was a movement of the thin sheet on the carrier). In the tablesbelow, a notation of “P” in the “Vacuum” column indicates that thesample did not fail as per the foregoing criteria.

(2) Wet process testing. Wet processes compatibility testing wasperformed using a Semitool model SRD-470S (available from AppliedMaterials, Santa Clara, Calif.). The testing consisted of 60 seconds 500rpm rinse, Q-rinse to 15 MOhm-cm at 500 rpm, 10 seconds purge at 500rpm, 90 seconds dry at 1800 rpm, and 180 seconds dry at 2400 rpm underwarm flowing nitrogen. Failure, as indicated by a notation of “F” in the“SRD” column of the tables below, was deemed to have occurred if therewas: (a) a loss of adhesion between the carrier and the thin sheet (byvisual inspection with the naked eye, wherein failure was deemed to haveoccurred if the thin sheet had fallen off of the carrier or waspartially debonded therefrom); (b) bubbling between the carrier and thethin sheet (as determined by visual inspection with the nakedeye—samples were photographed before and after the processing, and thencompared, failure was determined to have occurred if defects increasedin size by dimensions visible to the unaided eye); or (c) movement ofthe thin sheet relative to the carrier (as determined by visualobservation with the naked eye—samples were photographed before andafter testing, wherein failure was deemed to have occurred if there wasa movement of bond defects, e.g., bubbles, or if edges debonded, or ifthere was a movement of the thin sheet on the carrier); or (d)penetration of water under the thin sheet (as determined by visualinspection with an optical microscope at 50×, wherein failure wasdetermined to have occurred if liquid or residue was observable). In thetables below, a notation of “P” in the “SRD” column indicates that thesample did not fail as per the foregoing criteria.

(3) Temperature to 400° C. testing. 400° C. process compatibilitytesting was performed using an Alwin21 Accuthermo610 RTP (available fromAlwin21, Santa Clara Calif. A carrier with a thin sheet bonded theretowas heated in a chamber cycled from room temperature to 400° C. at 6.2°C./min, held at 400° C. for 600 seconds, and cooled at 1° C./min to 300°C. The carrier and thin sheet were then allowed to cool to roomtemperature. Failure, as indicated by a notation of “F” in the “400° C.”column of the tables below, was deemed to have occurred if there was:(a) a loss of adhesion between the carrier and the thin sheet (by visualinspection with the naked eye, wherein failure was deemed to haveoccurred if the thin sheet had fallen off of the carrier or waspartially debonded therefrom); (b) bubbling between the carrier and thethin sheet (as determined by visual inspection with the nakedeye—samples were photographed before and after the processing, and thencompared, failure was determined to have occurred if defects increasedin size by dimensions visible to the unaided eye); or (c) increasedadhesion between the carrier and the thin sheet whereby such increasedadhesion prevents debonding (by insertion of a razor blade between thethin sheet and carrier, and/or by sticking a piece of Kapton™ tape, 1″wide×6″ long with 2-3″ attached to 100 mm square thin glass (K102 seriesfrom Saint Gobain Performance Plastic, Hoosik N.Y.) to the thin sheetand pulling on the tape) of the thin sheet from the carrier withoutdamaging the thin sheet or the carrier, wherein a failure was deemed tohave occurred if there was damage to the thin sheet or carrier uponattempting to separate them, or if the thin sheet and carrier could notbe debonded by performance of either of the debonding methods.Additionally, after the thin sheet was bonded with the carrier, andprior to the thermal cycling, debonding tests were performed onrepresentative samples to determine that a particular material,including any associated surface treatment, did allow for debonding ofthe thin sheet from the carrier prior to the temperature cycling. In thetables below, a notation of “P” in the “400° C.” column indicates thatthe sample did not fail as per the foregoing criteria.

(4) Temperature to 600° C. testing. 600° C. process compatibilitytesting was performed using an Alwin21 Accuthermo610 RTP. A carrier witha thin sheet was heated in a chamber cycled from room temperature to600° C. at 9.5° C./min, held at 600° C. for 600 seconds, and then cooledat 1° C./min to 300° C. The carrier and thin sheet were then allowed tocool to room temperature. Failure, as indicated by a notation of “F” inthe “600° C.” column of the tables below, was deemed to have occurred ifthere was: (a) a loss of adhesion between the carrier and the thin sheet(by visual inspection with the naked eye, wherein failure was deemed tohave occurred if the thin sheet had fallen off of the carrier or waspartially debonded therefrom); (b) bubbling between the carrier and thethin sheet (as determined by visual inspection with the nakedeye—samples were photographed before and after the processing, and thencompared, failure was determined to have occurred if defects increasedin size by dimensions visible to the unaided eye); or (c) increasedadhesion between the carrier and the thin sheet whereby such increasedadhesion prevents debonding (by insertion of a razor blade between thethin sheet and carrier, and/or by sticking a piece of Kapton™ tape asdescribed above to the thin sheet and pulling on the tape) of the thinsheet from the carrier without damaging the thin sheet or the carrier,wherein a failure was deemed to have occurred if there was damage to thethin sheet or carrier upon attempting to separate them, or if the thinsheet and carrier could not be debonded by performance of either of thedebonding methods. Additionally, after the thin sheet was bonded withthe carrier, and prior to the thermal cycling, debonding tests wereperformed on representative samples to determine that a particularmaterial, and any associated surface treatment, did allow for debondingof the thin sheet from the carrier prior to the temperature cycling. Inthe tables below, a notation of “P” in the “600° C.” column indicatesthat the sample did not fail as per the foregoing criteria.

(5) Ultrasonic testing. Ultrasonic compatibility testing was performedby cleaning the article in a four tank line, wherein the article wasprocessed in each of the tanks sequentially from tank #1 to tank #4.Tank dimensions, for each of the four tanks, were 18.4″L×10″W×15″D. Twocleaning tanks (#1 and #2) contained 1% Semiclean KG available fromYokohama Oils and Fats Industry Co Ltd., Yokohama Japan in DI water at50° C. The cleaning tank #1 was agitated with a NEY prosonik 2 104 kHzultrasonic generator (available from Blackstone-NEY Ultrasonics,Jamestown, N.Y.), and the cleaning tank #2 was agitated with a NEYprosonik 2 104 kHz ultrasonic generator. Two rinse tanks (tank #3 andtank #4) contained DI water at 50° C. The rinse tank #3 was agitated byNEY sweepsonik 2D 72 kHz ultrasonic generator and the rinse tank #4 wasagitated by a NEY sweepsonik 2D 104 kHz ultrasonic generator. Theprocesses were carried out for 10 min in each of the tanks #1-4,followed by spin rinse drying (SRD) after the sample was removed fromtank #4. Failure, as indicated by a notation of “F” in the “Ultrasonic”column of the tables below, was deemed to have occurred if there was:(a) a loss of adhesion between the carrier and the thin sheet (by visualinspection with the naked eye, wherein failure was deemed to haveoccurred if the thin sheet had fallen off of the carrier or waspartially debonded therefrom); (b) bubbling between the carrier and thethin sheet (as determined by visual inspection with the nakedeye—samples were photographed before and after the processing, and thencompared, failure was determined to have occurred if defects increasedin size by dimensions visible to the unaided eye); or (c) formation ofother gross defects (as determined by visual inspection with opticalmicroscope at 50×, wherein failure was deemed to have occurred if therewere particles trapped between the thin glass and carrier that were notobserved before; or (d) penetration of water under the thin sheet (asdetermined by visual inspection with an optical microscope at 50×,wherein failure was determined to have occurred if liquid or residue wasobservable. In the tables below, a notation of “P” in the “Ultrasonic”column indicates that the sample did not fail as per the foregoingcriteria. Additionally, in the tables below, a blank in the “Ultrasonic”column indicates that the sample was not tested in this manner.

Preparation of Bonding Surfaces Via Hydroxyl Reduction by Heating

The benefit of modifying one or more of the bonding surfaces 14, 24 witha surface modification layer 30 so the article 2 is capable ofsuccessfully undergoing FPD processing (i.e., where the thin sheet 20remains bonded to the carrier 10 during processing, and yet may beseparated from the carrier 10 after processing, including hightemperature processing) was demonstrated by processing articles 2 havingglass carriers 10 and thin glass sheets 20 without a surfacemodification layer 30 therebetween. Specifically, first there was triedpreparation of the bonding surfaces 14, 24 by heating to reduce hydroxylgroups, but without a surface modification layer 30. The carriers 10 andthin sheets 20 were cleaned, the bonding surfaces 14 and 24 were bondedto one another, and then the articles 2 were tested. A typical cleaningprocess for preparing glass for bonding is the SC1 cleaning processwhere the glass is cleaned in a dilute hydrogen peroxide and base(commonly ammonium hydroxide, but tetramethylammonium hydroxidesolutions for example JT Baker JTB-100 or JTB-111 may also be used).Cleaning removes particles from the bonding surfaces, and makes thesurface energy known, i.e., it provides a base-line of surface energy.The manner of cleaning need not be SC1, other types of cleaning may beused, as the type of cleaning is likely to have only a very minor effecton the silanol groups on the surface. The results for various tests areset forth below in Table 1.

A strong but separable initial, room temperature or van der Waal and/orHydrogen-bond was created by simply cleaning a thin glass sheet of 100mm square×100 micron thick, and a glass carrier 150 mm diameter singlemean flat (SMF) wafer 0.50 or 0.63 mm thick, each comprising Eagle XG®display glass (an alkali-free, alumino-boro-silicate glass, having anaverage surface roughness Ra on the order of 0.2 nm, available fromCorning Incorporated, Corning, N.Y.). In this example, glass was cleaned10 min in a 65° C. bath of 40:1:2 DI water:JTB-111:Hydrogen peroxide.The thin glass or glass carrier may or may not have been annealed innitrogen for 10 min at 400° C. to remove residual water—the notation“400° C.” in the “Carrier” column or the “Thin Glass” column in Table 1below indicates that the sample was annealed in nitrogen for 10 minutesat 400° C. FPD process compatibility testing demonstrates this SC1-SC1initial, room temperature, bond is mechanically strong enough to passvacuum, SRD and ultrasonic testing. However, heating at 400° C. andabove created a permanent bond between the thin glass and carrier, i.e.,the thin glass sheet could not be removed from the carrier withoutdamaging either one or both of the thin glass sheet and carrier. Andthis was the case even for Example 1c, wherein each of the carrier andthe thin glass had an annealing step to reduce the concentration ofsurface hydroxyls. Accordingly, the above-described preparation of thebonding surfaces 14, 24 via heating alone and then bonding of thecarrier 10 and the thin sheet 12, without a surface modification layer30, is not a suitable controlled bond for FPD processes wherein thetemperature will be ≧400° C.

TABLE 1 process compatibility testing of SC1-treated glass bondingsurfaces Exam- Vac- 400 600 Ultra- ple Carrier Thin Glass uum SRD C. C.sonic 1a SC1 SC1 P P F F P 1b SC1, 400 C. SC1 P P F F P 1c SC1, 400 C.SC1, 400 C. P P F F P

Preparation of Bonding Surfaces by Hydroxyl Reduction and SurfaceModification Layer

Hydroxyl reduction, as by heat treatment for example, and a surfacemodification layer 30 may be used together to control the interaction ofbonding surfaces 14, 24. For example, the bonding energy (both van derWaals and/or Hydrogen-bonding at room temperature due to thepolar/dispersion energy components, and covalent bonding at hightemperature due to the covalent energy component) of the bondingsurfaces 14, 24 can be controlled so as to provide varying bond strengthfrom that wherein room-temperature bonding is difficult, to thatallowing easy room-temperature bonding and separation of the bondingsurfaces after high temperature processing, to that which—after hightemperature processing—prevents the surfaces from separating withoutdamage. In some applications, it may be desirable to have no, or veryweak bonding (as when the surfaces are in a “non-bonding” region, as a“non-bonding” region is described in the thin sheet/carrier concept ofUS '727, and as described below). In other applications, for exampleproviding a re-usable carrier for FPD processes and the like (whereinprocess temperatures ≧500° C., or ≧600° C., and up to 650° C., may beachieved), it is desirable to have sufficient van der Waals and/orHydrogen-bonding, at room temperature to initially put the thin sheetand carrier together, and yet prevent or limit high temperature covalentbonding. For still other applications, it may be desirable to havesufficient room temperature boding to initially put the thin sheet andcarrier together, and also to develop strong covalent bonding at hightemperature (as when the surfaces are in a “bonding region”, as “bondingregion” is described in the thin sheet/carrier concept of US '727, andas discussed below). Although not wishing to be bound by theory, in someinstances the surface modification layer may be used to control roomtemperature bonding by which the thin sheet and carrier are initiallyput together, whereas the reduction of hydroxyl groups on the surface(as by heating the surface, or by reaction of the hydroxyl groups withthe surface modification layer, for example) may be used to control thecovalent bonding, particularly that at high temperatures.

A material for the surface modification layer 30 may provide a bondingsurface 14, 24 with an energy (for example, and energy <40 mJ/m², asmeasured for one surface, and including polar and dispersion components)whereby the surface produces only weak bonding. In one example,hexamethyldisilazane (HMDS) may be used to create this low energysurface by reacting with the surface hydroxyls to leave a trimethylsilyl(TMS) terminated surface. HMDS as a surface modification layer may beused together with surface heating to reduce the hydroxyl concentrationto control both room temperature and high temperature bonding. Bychoosing a suitable bonding surface preparation for each bonding surface14, 24, there can be achieved articles having a range of capabilities.More specifically, of interest to providing a reusable carrier for LTPSprocessing, there can be achieved a suitable bond between a thin glasssheet 20 and a glass carrier 10 so as to survive (or pass) each of thevacuum SRD, 400° C. (parts a and c), and 600° C. (parts a and c),processing tests.

In one example, following SC1 cleaning by HMDS treatment of both thinglass and carrier creates a weakly bonded surface which is challengingto bond at room temperature with van der Waals (and/or hydrogen bonding)forces. Mechanical force is applied to bond the thin glass to thecarrier. As shown in example 2a of Table 2, this bonding is sufficientlyweak that deflection of the carrier is observed in vacuum testing andSRD processing, bubbling (likely due to outgassing) was observed in 400°C. and 600° C. thermal processes, and particulate defects were observedafter ultrasonic processing.

In another example, HMDS treatment of just one surface (carrier in theexample cited) creates stronger room temperature adhesion which survivesvacuum and SRD processing. However, thermal processes at 400° C. andabove permanently bonded the thin glass to the carrier. This is notunexpected as the maximum surface coverage of the trimethylsilyl groupson silica has been calculated by Sindorf and Maciel in J. Phys. Chem.1982, 86, 5208-5219 to be 2.8/nm² and measured by Suratwala et. al. inJournal of Non-Crystalline Solids 316 (2003) 349-363 as 2.7/nm², vs. ahydroxyl concentration of 4.6-4.9/nm² for fully hydroxylated silica.That is, although the trimethylsilyl groups do bond with some surfacehydroxyls, there will remain some un-bonded hydroxyls. Thus one wouldexpect condensation of surface silanol groups to permanently bond thethin glass and carrier given sufficient time and temperature.

A varied surface energy can be created by heating the glass surface toreduce the surface hydroxyl concentration prior to HMDS exposure,leading to an increased polar component of the surface energy. This bothdecreases the driving force for formation of covalent Si—O—Si bonds athigh temperature and leads to stronger room-temperature bonding, forexample, van der Waal (and/or hydrogen) bonding. FIG. 4 shows thesurface energy of an Eagle XG® display glass carrier after annealing,and after HMDS treatment. Increased annealing temperature prior to HMDSexposure increases the total (polar and dispersion) surface energy (line402) after HMDS exposure by increasing the polar contribution (line404). It is also seen that the dispersion contribution (line 406) to thetotal surface energy remains largely unchanged by the heat treatment.Although not wishing to be bound by theory, increasing the polarcomponent of, and thereby the total, energy in the surface after HMDStreatment appears to be due to there being some exposed glass surfaceareas even after HMDS treatment because of sub-monolayer TMS coverage bythe HMDS.

In example 2b, the thin glass sheet was heated at a temperature of 150°C. in a vacuum for one hour prior to bonding with the non-heat-treatedcarrier having a coating of HMDS. This heat treatment of the thin glasssheet was not sufficient to prevent permanent bonding of the thin glasssheet to the carrier at temperatures ≧400° C.

As shown in examples 2c-2e of Table 2, varying the annealing temperatureof the glass surface prior to HMDS exposure can vary the bonding energyof the glass surface so as to control bonding between the glass carrierand the thin glass sheet.

In example 2c, the carrier was annealed at a temperature of 190° C. invacuum for 1 hour, followed by HMDS exposure to provide surfacemodification layer 30. Additionally, the thin glass sheet was annealedat 450° C. in a vacuum for 1 hour before bonding with the carrier. Theresulting article survived the vacuum, SRD, and 400° C. tests (parts aand c, but did not pass part b as there was increased bubbling), butfailed the 600° C. test. Accordingly, although there was increasedresistance to high temperature bonding as compared with example 2b, thiswas not sufficient to produce an article for processing at temperatures≧600° C. (for example LTPS processing) wherein the carrier is reusable.

In example 2d, the carrier was annealed at a temperature of 340° C. in avacuum for 1 hour, followed by HMDS exposure to provide surfacemodification layer 30. Again, the thin glass sheet was annealed at 450°C. for 1 hour in a vacuum before bonding with the carrier. The resultswere similar to those for example 2c, wherein the article survived thevacuum, SRD, and 400° C. tests (parts a and c, but did not pass part bas there was increased bubbling), but failed the 600° C. test.

As shown in example 2e, annealing both thin glass and carrier at 450° C.in vacuum for 1 hr, followed by HMDS exposure of the carrier, and thenbonding of the carrier and thin glass sheet, improves the temperatureresistance to permanent bonding. An anneal of both surfaces to 450° C.prevents permanent bonding after RTP annealing at 600° C. for 10 min,that is, this sample passed the 600° C. processing test (parts a and c,but did not pass part b as there was increased bubbling; a similarresult was found for the 400° C. test).

TABLE 2 process compatibility testing of HMDS surface modificationlayers Exam- Vac- 400 600 Ultra- ple Carrier Thin Glass uum SRD C. C.sonic 2a SC1, HMDS SC1, HMDS F F P P F 2b SC1, HMDS SC1, 150 C. P P F F2c SC1, 190 C., SC1, 450 C. P P P F HMDS 2d SC1, 340 C., SC1, 450 C. P PP F HMDS 2e SC1, 450 C., SC1, 450 C. P P P P HMDS

In Examples 2a to 2e above, each of the carrier and the thin sheet wereEagle XG® glass, wherein the carrier was a 150 mm diameter SMF wafer 630microns thick and the thin sheet was 100 mm square 100 microns thick TheHMDS was applied by pulse vapor deposition in a YES-5 HMDS oven(available from Yield Engineering Systems, San Jose Calif.) and was oneatomic layer thick (i.e., about 0.2 to 1 nm), although the surfacecoverage may be less than one monolayer, i.e., some of the surfacehydroxyls are not covered by the HMDS as noted by Maciel and discussedabove. Because of the small thickness in the surface modification layer,there is little risk of outgassing which can cause contamination in thedevice fabrication. Further, because the surface modification layer didnot appear to degrade, again, there is even less risk of outgassing.Also, as indicated in Table 2 by the “SC1” notation, each of thecarriers and thin sheets were cleaned using an SC1 process prior to heattreating or any subsequent HMDS treatment.

A comparison of example 2a with example 2b shows that the bonding energybetween the thin sheet and the carrier can be controlled by varying thenumber of surfaces which include a surface modification layer. Andcontrolling the bonding energy can be used to control the bonding forcebetween two bonding surfaces. Also, a comparison of examples 2b-2e,shows that the bonding energy of a surface can be controlled by varyingthe parameters of a heat treatment to which the bonding surface issubjected before application of a surface modification material. Again,the heat treatment can be used to reduce the number of surface hydroxylsand, thus, control the degree of covalent bonding, especially that athigh temperatures.

Other materials, that may act in a different manner to control thesurface energy on a bonding surface, may be used for the surfacemodification layer 30 so as to control the room temperature and hightemperature bonding forces between two surfaces. For example, a reusablecarrier can also be created if one or both bonding surfaces are modifiedto create a moderate bonding force with a surface modification layerthat either covers, or sterically hinders species for example hydroxylsto prevent the formation at elevated temperature of strong permanentcovalent bonds between carrier and thin sheet. One way to create atunable surface energy, and cover surface hydroxyls to prevent formationof covalent bonds, is deposition of plasma polymer films, for examplefluoropolymer films. Plasma polymerization deposits a thin polymer filmunder atmospheric or reduced pressure and plasma excitation (DC or RFparallel plate, Inductively Coupled Plasma (ICP) Electron CyclotronResonance (ECR) downstream microwave or RF plasma) from source gases forexample fluorocarbon sources (including CF4, CHF3, C2F6, C3F6, C2F2,CH3F, C4F8, chlorofluoro carbons, or hydrochlorofluoro carbons),hydrocarbons for example alkanes (including methane, ethane, propane,butane), alkenes (including ethylene, propylene), alkynes (includingacetylene), and aromatics (including benzene, toluene), hydrogen, andother gas sources for example SF6. Plasma polymerization creates a layerof highly cross-linked material. Control of reaction conditions andsource gases can be used to control the film thickness, density, andchemistry to tailor the functional groups to the desired application.

FIG. 5 shows the total (line 502) surface energy (including polar (line504) and dispersion (line 506) components) of plasma polymerizedfluoropolymer (PPFP) films deposited from CF4-C4F8 mixtures with anOxford ICP380 etch tool (available from Oxford Instruments, OxfordshireUK). The films were deposited onto a sheet of Eagle XG® glass, andspectroscopic ellipsometry showed the films to be 1-10 nm thick. As seenfrom FIG. 5, glass carriers treated with plasma polymerizedfluoropolymer films containing less than 40% C4F8 exhibit a surfaceenergy >40 mJ/m² and produce controlled bonding between the thin glassand carrier at room temperature by van der Waal or hydrogen bonding.Facilitated bonding is observed when initially bonding the carrier andthin glass at room temperature. That is, when placing the thin sheetonto the carrier, and pressing them together at a point, a wave fronttravels across the carrier, but at a lower speed than is observed forSC1 treated surfaces having no surface modification layer thereon. Thecontrolled bonding is sufficient to withstand all standard FPD processesincluding vacuum, wet, ultrasonic, and thermal processes up to 600° C.,that is this controlled bonding passed the 600° C. processing testwithout movement or delamination of the thin glass from the carrier.De-bonding was accomplished by peeling with a razor blade and/or Kapton™tape as described above. The process compatibility of two different PPFPfilms (deposited as described above) is shown in Table 3. PPFP 1 ofexample 3a was formed with C4F8/(C4F8+CF4)=0, that is, formed withCF4/H2 and not C4F8, and PPFP 2 of example 3b was deposited withC4F8/(C4F8+CF4)=0.38. Both types of PPFP films survived the vacuum, SRD,400° C. and 600° C. processing tests. However, delamination is observedafter 20 min of ultrasonic cleaning of PPFP 2 indicating insufficientadhesive force to withstand such processing. Nonetheless, the surfacemodification layer of PPFP2 may be useful for some applications, aswhere ultrasonic processing is not necessary.

TABLE 3 process compatibility testing of PPFP surface modificationlayers Exam- Vac- 400 600 Ultra- ple Carrier Thin Glass uum SRD C. C.sonic 3a PPFP 1 SC1, 150 C. P P P P P 3b PPFP2 SC1, 150 C. P P P P F

In Examples 3a and 3b above, each of the carrier and the thin sheet wereEagle XG® glass, wherein the carrier was a 150 mm diameter SMF wafer 630microns thick and the thin sheet was 100 mm square 100 microns thick.Because of the small thickness in the surface modification layer, thereis little risk of outgassing which can cause contamination in the devicefabrication. Further, because the surface modification layer did notappear to degrade, again, there is even less risk of outgassing. Also,as indicated in Table 3, each of the thin sheets was cleaned using anSC1 process prior to heat treating at 150° C. for one hour in a vacuum.

Still other materials, that may function in a different manner tocontrol surface energy, may be used as the surface modification layer tocontrol the room temperature and high temperature bonding forces betweenthe thin sheet and the carrier. For example, a bonding surface that canproduce controlled bonding can be created by silane treating a glasscarrier and/or glass thin sheet. Silanes are chosen so as to produce asuitable surface energy, and so as to have sufficient thermal stabilityfor the application. The carrier or thin glass to be treated may becleaned by a process for example O2 plasma or UV-ozone, and SC1 orstandard clean two (SC2, as is known in the art) cleaning to removeorganics and other impurities (metals, for example) that would interferewith the silane reacting with the surface silanol groups. Washes basedon other chemistries may also be used, for example, HF, or H2SO4 washchemistries. The carrier or thin glass may be heated to control thesurface hydroxyl concentration prior to silane application (as discussedabove in connection with the surface modification layer of HMDS), and/ormay be heated after silane application to complete silane condensationwith the surface hydroxyls. The concentration of unreacted hydroxylgroups after silanization may be made low enough prior to bonding as toprevent permanent bonding between the thin glass and carrier attemperatures ≧400° C., that is, to form a controlled bond. This approachis described below.

Example 4a

A glass carrier with its bonding surface O2 plasma and SC1 treated wasthen treated with 1% dodecyltriethoxysilane (DDTS) in toluene, andannealed at 150° C. in vacuum for 1 hr to complete condensation. DDTStreated surfaces exhibit a surface energy of 45 mJ/m². As shown in Table4, a glass thin sheet (having been SC1 cleaned and heated at 400° C. ina vacuum for one hour) was bonded to the carrier bonding surface havingthe DDTS surface modification layer thereon. This article survived wetand vacuum process tests but did not survive thermal processes over 400°C. without bubbles forming under the carrier due to thermaldecomposition of the silane. This thermal decomposition is expected forall linear alkoxy and chloro alkylsilanes R1_(x)Si(OR2)_(y)(Cl)_(z)where x=1 to 3, and y+z=4−x except for methyl, dimethyl, and trimethylsilane (x=1 to 3, R1=CH₃) which produce coatings of good thermalstability.

Example 4b

A glass carrier with its bonding surface O2 plasma and SC1 treated wasthen treated with 1% 3,3,3, trifluoropropyltritheoxysilane (TFTS) intoluene, and annealed at 150° C. in vacuum for 1 hr to completecondensation. TFTS treated surfaces exhibit a surface energy of 47mJ/m². As shown in Table 4, a glass thin sheet (having been SC1 cleanedand then heated at 400° C. in a vacuum for one hour) was bonded to thecarrier bonding surface having the TFTS surface modification layerthereon. This article survived the vacuum, SRD, and 400° C. processtests without permanent bonding of the glass thin sheet to the glasscarrier. However, the 600° C. test produced bubbles forming under thecarrier due to thermal decomposition of the silane. This was notunexpected because of the limited thermal stability of the propyl group.Although this sample failed the 600° C. test due to the bubbling, thematerial and heat treatment of this example may be used for someapplications wherein bubbles and the adverse effects thereof, forexample reduction in surface flatness, or increased waviness, can betolerated.

Example 4c

A glass carrier with its bonding surface O2 plasma and SC1 treated wasthen treated with 1% phenyltriethoxysilane (PTS) in toluene, andannealed at 200° C. in vacuum for 1 hr to complete condensation. PTStreated surfaces exhibit a surface energy of 54 mJ/m². As shown in Table4, a glass thin sheet (having been SC1 cleaned and then heated at 400°C. in a vacuum for one hour) was bonded to the carrier bonding surfacehaving the PTS surface modification layer. This article survived thevacuum, SRD, and thermal processes up to 600° C. without permanentbonding of the glass thin sheet with the glass carrier.

Example 4d

A glass carrier with its bonding surface O2 plasma and SC1 treated wasthen treated with 1% diphenyldiethoxysilane (DPDS) in toluene, andannealed at 200° C. in vacuum for 1 hr to complete condensation. DPDStreated surfaces exhibit a surface energy of 47 mJ/m². As shown in Table4, a glass thin sheet (having been SC1 cleaned and then heated at 400°C. in a vacuum for one hour) was bonded to the carrier bonding surfacehaving the DPDS surface modification layer. This article survived thevacuum and SRD tests, as well as thermal processes up to 600° C. withoutpermanent bonding of the glass thin sheet with the glass carrier

Example 4e

A glass carrier having its bonding surface O2 plasma and SC1 treated wasthen treated with 1% 4-pentafluorophenyltriethoxysilane (PFPTS) intoluene, and annealed at 200° C. in vacuum for 1 hr to completecondensation. PFPTS treated surfaces exhibit a surface energy of 57mJ/m². As shown in Table 4, a glass thin sheet (having been SC1 cleanedand then heated at 400° C. in a vacuum for one hour) was bonded to thecarrier bonding surface having the PFPTS surface modification layer.This article survived the vacuum and SRD tests, as well as thermalprocesses up to 600° C. without permanent bonding of the glass thinsheet with the glass carrier.

TABLE 4 process compatibility testing of silane surface modificationlayers Exam- Vac- 400 600 ple Carrier Thin Glass uum SRD C. C. 4a SC1,DDTS SC1, 400 C. P P F F 4b SC1, TFTS SC1, 400 C. P P P F 4c SC1, PTSSC1, 400 C. P P P P 4d SC1, DPDS SC1, 400 C. P P P P 4e SC1, PFPTS SC1,400 C. P P P P

In Examples 4a to 4e above, each of the carrier and the thin sheet wereEagle XG® glass, wherein the carrier was a 150 mm diameter SMF wafer 630microns thick and the thin sheet was 100 mm square 100 microns thick.The silane layers were self-assembled monolayers (SAM), and thus were onthe order of less than about 2 nm thick. In the above examples, the SAMwas created using an organosilane with an aryl or alkyl non-polar tailand a mono, di, or tri-alkoxide head group. These react with the silnaolsurface on the glass to directly attach the organic functionality.Weaker interactions between the non-polar head groups organize theorganic layer. Because of the small thickness in the surfacemodification layer, there is little risk of outgassing which can causecontamination in the device fabrication. Further, because the surfacemodification layer did not appear to degrade in examples 4c, 4d, and 4e,again, there is even less risk of outgassing. Also, as indicated inTable 4, each of the glass thin sheets was cleaned using an SC1 processprior to heat treating at 400° C. for one hour in a vacuum.

As can be seen from a comparison of examples 4a-4e, controlling surfaceenergy of the bonding surfaces to be above 40 mJ/m² so as to facilitatethe initial room temperature bonding is not the only consideration tocreating a controlled bond that will withstand FPD processing and stillallow the thin sheet to be removed from the carrier without damage.Specifically, as seen from examples 4a-4e, each carrier had a surfaceenergy above 40 mJ/m², which facilitated initial room temperaturebonding so that the article survived vacuum and SRD processing. However,examples 4a and 4b did not pass 600° C. processing test. As noted above,for certain applications, it is also important for the bond to surviveprocessing up to high temperatures (for example, ≧400° C., ≧500° C., or≧600° C., up to 650° C., as appropriate to the processes in which thearticle is designed to be used) without degradation of the bond to thepoint where it is insufficient to hold the thin sheet and carriertogether, and also to control the covalent bonding that occurs at suchhigh temperatures so that there is no permanent bonding between the thinsheet and the carrier. As shown by the examples in Table 4, aromaticsilanes, in particular phenyl silanes, are useful for providing acontrolled bond that will facilitate initial room temperature bonding,and that will withstand FPD processing and still allow the thin sheet tobe removed from the carrier without damage.

The above-described separation in examples 4, 3, and 2, is performed atroom temperature without the addition of any further thermal or chemicalenergy to modify the bonding interface between the thin sheet andcarrier. The only energy input is mechanical pulling and/or peelingforce.

The materials described above in examples 3 and 4 can be applied to thecarrier, to the thin sheet, or to both the carrier and thin sheetsurfaces that will be bonded together.

Uses of Controlled Bonding

To Provide a Controlled Bonding Area

One use of controlled bonding via surface modification layers (includingmaterials and the associated bonding surface heat treatments) is toprovide a controlled bonding area, between a glass carrier and a glassthin sheet. More specifically, with the use of the surface modificationlayers an area of controlled bonding can be formed wherein a sufficientseparation force can separate the thin sheet portion from the carrierwithout damage to either the thin sheet or the carrier caused by thebond, yet there is maintained throughout processing a sufficient bondingforce to hold the thin sheet relative to the carrier. With reference toFIG. 6, a glass thin sheet 20 may be bonded to a glass carrier 10 by abonded area 40. In the bonded area 40, the carrier 10 and thin sheet 20are covalently bonded to one another so that they act as a monolith.Additionally, there are controlled bonding areas 50 having perimeters52, wherein the carrier 10 and thin sheet 20 are connected, but may beseparated from one another, even after high temperature processing, e.g.processing at temperatures ≧600° C. Although ten controlled bondingareas 50 are shown in FIG. 6, any suitable number, including one, may beprovided. The surface modification layers 30, including the materialsand bonding surface heat treatments, as exemplified by the examples 2a,2e, 3a, 3b, 4c, 4d, and 4e, above, may be used to provide the controlledbonding areas 50 between the carrier 10 and the thin sheet 20.Specifically, these surface modification layers may be formed within theperimeters 52 of controlled bonding areas 50 either on the carrier 10 oron the thin sheet 20. Accordingly, when the article 2 is processed athigh temperature, either to form covalent bonding in the bonding area 40or during device processing, there can be provided a controlled bondbetween the carrier 10 and the thin sheet 20 within the areas bounded byperimeters 52 whereby a separation force may separate (withoutcatastrophic damage to the thin sheet or carrier) the thin sheet andcarrier in this region, yet the thin sheet and carrier will notdelaminate during processing, including ultrasonic processing. Thecontrolled bonding of the present application, as provided by thesurface modification layers and any associated heat treatments, is thusable to improve upon the carrier concept in US '727. Specifically,Although the carriers of US '727 were demonstrated to survive FPDprocessing, including high temperature processing ≧about 600° C. withtheir bonded peripheries and non-bonded center regions, ultrasonicprocesses for example wet cleans and resist strip processing remainedchallenging. Specifically, pressure waves in the solution were seen toinduce sympathic vibrations in the thin glass in the non-bonding region(as non-bonding was described in US '727), as there was little or noadhesive force bonding the thin glass and carrier in that region.Standing waves in the thin glass can be formed, wherein these waves maycause vibrations that can lead to breakage of the thin glass at theinterface between the bonded and non-bonded regions if the ultrasonicagitation is of sufficient intensity. This problem can be eliminated byminimizing the gap between the thin glass and the carrier and byproviding sufficient adhesion, or controlled bonding between the carrier20 and thin glass 10 in these areas 50. Surface modification layers(including materials and any associated heat treatments as exemplifiedby examples 2a, 2e, 3a, 3b, 4c, 4d, and 4e) of the bonding surfacescontrol the bonding energy so as to provide a sufficient bond betweenthe thin sheet 20 and carrier 10 to avoid these unwanted vibrations inthe controlled bonding region.

Then, during extraction of the desired parts 56 having perimeters 57,the portions of thin sheet 20 within the perimeters 52 may simply beseparated from the carrier 10 after processing and after separation ofthe thin sheet along perimeters 57. Because the surface modificationlayers control bonding energy to prevent permanent bonding of the thinsheet with the carrier, they may be used for processes whereintemperatures are ≧600° C. Of course, although these surface modificationlayers may control bonding surface energy during processing attemperatures ≧600° C., they may also be used to produce a thin sheet andcarrier combination that will withstand processing at lowertemperatures, and may be used in such lower temperature applications.Moreover, where the thermal processing of the article will not exceed400° C., surface modification layers as exemplified by the examples 2c,2d, 4b may also be used—in some instances, depending upon the otherprocess requirements—in this same manner to control bonding surfaceenergy.

To Provide a Bonding Area

A second use of controlled bonding via surface modification layers(including materials and any associated bonding surface heat treatment)is to provide a bonding area between a glass carrier and a glass thinsheet. With reference to FIG. 6, a glass thin sheet 20 may be bonded toa glass carrier 10 by a bonded area 40.

In one embodiment of the second use, the bonded area 40, the carrier 10and thin sheet 20 may be covalently bonded to one another so that theyact as a monolith. Additionally, there are controlled bonding areas 50having perimeters 52, wherein the carrier 10 and thin sheet 20 arebonded to one another sufficient to withstand processing, and stillallow separation of the thin sheet from the carrier even after hightemperature processing, e.g. processing at temperatures ≧600° C.Accordingly, surface modification layers 30 (including materials andbonding surface heat treatments) as exemplified by the examples 1a, 1b,1c, 2b, 2c, 2d, 4a, and 4b above, may be used to provide the bondingareas 40 between the carrier 10 and the thin sheet 20. Specifically,these surface modification layers and heat treatments may be formedoutside of the perimeters 52 of controlled bonding areas 50 either onthe carrier 10 or on the thin sheet 20. Accordingly, when the article 2is processed at high temperature, or is treated at high temperature toform covalent bonds, the carrier and the thin sheet 20 will bond to oneanother within the bonding area 40 outside of the areas bounded byperimeters 52. Then, during extraction of the desired parts 56 havingperimeters 57, when it is desired to dice the thin sheet 20 and carrier10, the article may be separated along lines 5 because these surfacemodification layers and heat treatments covalently bond the thin sheet20 with the carrier 10 so they act as a monolith in this area. Becausethe surface modification layers provide permanent covalent bonding ofthe thin sheet with the carrier, they may be used for processes whereintemperatures are ≧600° C. Moreover, where the thermal processing of thearticle, or of the initial formation of the bonding area 40, will be≧400° C. but less than 600° C., surface modification layers, asexemplified by the materials and heat treatments in example 4a may alsobe used in this same manner.

In a second embodiment of the second use, in the bonded area 40, thecarrier 10 and thin sheet 20 may be bonded to one another by controlledbonding via various surface modification layers described above.Additionally, there are controlled bonding areas 50, having perimeters52, wherein the carrier 10 and thin sheet 20 are bonded to one anothersufficient to withstand processing, and still allow separation of thethin sheet from the carrier even after high temperature processing, e.g.processing at temperatures ≧600° C. Accordingly, if processing will beperformed at temperatures up to 600° C., and it is desired not to have apermanent or covalent bond in area 40, surface modification layers 30(including materials and bonding surface heat treatments) as exemplifiedby the examples 2e, 3a, 3b, 4c, 4d, and 4e above, may be used to providethe bonding areas 40 between the carrier 10 and the thin sheet 20.Specifically, these surface modification layers and heat treatments maybe formed outside of the perimeters 52 of controlled bonding areas 50,and may be formed either on the carrier 10 or on the thin sheet 20. Thecontrolled bonding areas 50 may be formed with the same, or with adifferent, surface modification layer as was formed in the bonding area40. Alternatively, if processing will be performed at temperatures onlyup to 400° C., and it is desired not to have a permanent or covalentbond in area 40, surface modification layers 30 (including materials andbonding surface heat treatments) as exemplified by the examples 2c, 2d,2e, 3a, 3b, 4b, 4c, 4d, 4e, above, may be used to provide the bondingareas 40 between the carrier 10 and the thin sheet 20.

Instead of controlled bonding in areas 50, there may be non-bondingregions in areas 50, wherein the non-bonding regions may be areas ofincreased surface roughness as described in US '727, or may be providedby surface modification layers as exemplified by example 2a.

Simplified Manner of Making an Article

A third use of various ones of the above-described surface modificationlayers, including materials and their associated surface treatments, maybe used to provide a simplified manner of making an article having acovalently bonded perimeter, i.e., one having a hermetic seal around itsperimeter so as to prevent ingress of fluids that may undesirablycontaminate downstream processes. Alternatively, or in addition to, acovalently bonded perimeter, covalent bonding between the carrier andthin sheet may be desired in certain areas of the article, and notdesired in other areas of the article (wherein controlled bonding may bedesired to allow sections of the thin sheet to be removed from thecarrier without damage to either). Again, various ones of theabove-described surface modification layers, including materials andtheir associated surface treatments, may be used to provide suchpatterned covalent bonding areas, and patterned controlled bondingareas.

First Embodiment of the Third Use

A first embodiment of making an article 2 having a bonding area 40 thatincludes permanent covalent bonding, and a controlled bonding area 50,will now be described with reference to FIGS. 7-10. For example, to makearticle 2, a surface modification layer 30 is provided on a glasscarrier 10. For the sake of ease in illustration the surfacemodification layer 30 is shown and described as being provided on thecarrier 10. However, a surface modification layer 30 may be provided onthe carrier 10, the glass thin sheet 20, or both of them. When providedon both the carrier 10 and the thin sheet 20, the surface modificationlayers are preferably of the same material, although they need not be.The surface modification layer 30 is provided over the entire bondingsurface 14 of the carrier 10. The surface modification layer may beprovided on the carrier 10 according to any one of the materials andsurface treatments as set forth in Examples 2a (as when ultrasonicprocessing is not required or its effects can be tolerated within thecontrolled bonding areas 50), and 2b-2d, for example. As necessary, thebonding surface 24 of the carrier 20 may be prepared as per the surfacepreparation set forth in Examples 2a (again, with the above-notedconditions) and 2b-d. The thin sheet 20 is then connected with thecarrier 10 via the surface modification layer 30, which providescontrolled bonding. At this stage the arrangement will appear in crosssection as shown in FIG. 8, and the connection between the carrier 10and the thin sheet 20 is one of van der Waals or hydrogen bonding atroom temperature such that the carrier and sheet may be separated fromone another without damage to at least the thin sheet. As shown in FIGS.7 and 8, the bonding surface area of the carrier is the same size as thebonding surface area of thin sheet, however, such need not be the case.Instead, the surface area of the carrier may be larger than the surfacearea of the thin sheet, or vice versa.

The arrangement of the carrier 10, the surface modification layer 30,and the thin sheet 20 is then subjected to a process for removing aportion of the surface modification layer 30, i.e., that portion ofsurface modification layer 30 residing in the area in which there isdesired to form a bonding area 40 including permanent covalent bonds. Inthe example shown in FIGS. 7-10, the desired bonding area 40 is aroundthe perimeter of the article 2. Accordingly, the perimeter portion ofthe surface modification layer 30 is removed to form respective, andadjoining, exposed portions 19, 29 on the carrier 10 and thin sheet 20.The article 2 appears in cross section as shown in FIG. 9, for example.The exposed portions 19, 29 are adjoining in that they are both disposedin a position on the area of the bonding surfaces 14, 24, wherein atleast a portion of each faces the other across a small gap. Although itdoes not appear as being the case from the figures, the exposed portions19 and 29 are really in close proximity to one another, due to the smallthickness of the surface modification layer (i.e., on the order ofnanometers, typically 0.1 to 2.0 nm, up to 10 nm, and in some cases upto 100 nm).

The surface modification layer 30 may be removed by various techniques,for example, by exposing the article 2 to O2 plasma, laser radiation, UVradiation, heating, or a combination thereof. The technique used toremove a portion of the surface modification layer 30 may depend uponthe material from which that layer is made. For example, a particularlyeffective manner of removing a surface modification layer 30 of HMDS isby O2 plasma, which oxidizes the HMDS. Other means of oxidation thatwork are downstream oxygen plasma, and UV-Ozone, for example. If theremoval is also performed under vacuum, the oxidized HMDS is easilyremoved from between the carrier 10 and thin sheet 20, which may assistin forming a stronger covalent bond between the exposed portions 19, 29.

Other materials—that may be used for the controlled bonding area, andthat may be removed from the perimeter, or other areas, to subsequentlyform bonding areas 40—include, for example: alkyl silanes; fluoro-alkylsilanes; aromatic silanes; fluoro or chloro aromatic silanes;fluorinated organics for example, Teflon, and fluoropolymers andfluorinated aromatic silanes known to produce low energy surfaces;silanes that produce trimethylsilyl or methylsilyl terminated surfacesuch as hexamethyldisilazane, 1,1,3,3-Tetramethyldisilazane,2,2,4,4,6,6-Hexamethylcyclotrisilazane,1,1,3,3-Tetramethyl-1,3-diphenyldisilazane,1,3-Dimethyl-1,1,3,3-tetraphenyldisilazane methoxytrimethylsilane,ethoxytrimethylsilane chlorotrimethylsilane, dimethoxydimethylsilane,and dichlorodmethylsilane; silanes that produce an aromatic terminatedsurface or fluorinated aromatic surface such as phenyltrimethoxysilane,phenyltriethoxysilane, diphenyldimethoxysilane, chlorophenyl silanes,diphenyldiethoxysilane, diphenylmethylmethoxyphenylsilane,chlorodimethyl(pentafluorophenyl)silane,pentafluorophenyltrimethoxysilane, pentafluorophenyltriethoxysilanephenyldimethylmethoxysilane anddimethylmethoxy(pentafluorophenyl)silane; silanes with one resultingsilanol, bis and or tris-silanols may also work; for thermal stability,there are also some halogen substituted aromatic silanes; Diamond likecarbon; fluorinated diamond like carbon; and graphene.

Because the carrier 10 and thin sheet 20 remain connected by thenon-removed portion of the surface modification layer 30 throughout theremoval of the portion of the surface modification layer 30 from bondingarea 40, the portion of the surface modification layer in the controlledbonding area 50 is protected from contamination from any debrisassociated with the removal. Accordingly, there is provided a highquality controlled bonding area 50. Moreover, this technique self-alignsthe exposed portions 19, 29 for covalent bonding as it removes thesurface modification layer from the perimeter inward with the carrier 10and thin sheet 20 already van der Walls or Hydrogen bonded together.

Next, the article is heated to a temperature sufficient to providecovalent bonding between the exposed portions 19, 29 to form a bondingarea 40. For example, in the case of a surface modification layeraccording to example 2b, the article would be heated to ≧400° C.,whereas in the case of a surface modification layer according to example2c or 2d, the article would be heated to ≧600° C., wherein the practicalupper limit is near the strain point of the glass in the carrier, orthat in the thin sheet, whichever strain point is lower. After heatingto the appropriate temperature, the article 2 will appear in crosssection as shown in FIG. 10, wherein the carrier 10 and thin sheet 20have permanently covalently bonded in the bonding area 40 so as tobehave as a monolithic sheet of glass.

The desired parts 56 may then be formed on the thin sheet 20 in thecontrolled bonding area 50. When it is desired to remove the desiredparts 56, the covalently bonded portions, i.e., the perimeter bondingarea 40 may simply be sliced off of the article. The entire thin sheetremaining after removing the covalently bonded portion may then beremoved from the carrier, and separated to form individual desired parts56. Alternatively, the remaining thin sheet may be removed in two ormore pieces by first separating the thin sheet into portions, and thenremoving each of the portions as desired.

Alternatively, to make the desired number of desired parts 56 on onearticle 2, there may first be made a desired number of controlledbonding areas 50 surrounded by bonded contour lines 42. See FIG. 11. Thebonded contour lines 42 may be selectively formed by selectively tracinga laser in the desired shape to locally heat the surface modificationlayer 30 to a sufficient predetermined temperature to selectively ablatethe surface modification layer to form exposed portions (similar toexposed portions 19, 29) on the carrier 10 and thin sheet 20. Thecarrier 10 and thin sheet 20 may then be covalently bonded to formadditional bonding regions along the contour lines 42.

The article 2 may then be processed so as to form devices within theareas defined by the contour lines 42. After device processing, thedesired parts 56 may be separated from the carrier 10 by any suitablemanner. For example, a vent may be formed through the thickness 28 ofthe thin sheet 20 to form a perimeter vent 57. The perimeter vent 57 maybe formed, for example, by a mechanical scribe and break process, by alaser scribe and break process, by propagation of a full body vent vialaser, or by a full body laser cut. If it is desired to slide thedesired parts 56 off of the carrier, or to provide an exposed edge ofthe parts 56 to facilitate peeling, the article 2 may first be dicedinto any smaller number of pieces, by dicing between appropriate ones ofadjacent contour lines 42, e.g., along any pattern or sub-set of dashedlines 5. Alternatively, the article 2 may be diced along lines made soas to intersect with the perimeter vent defining the perimeter 57 of thedesired part 56.

The latter method of forming the desired parts 56 within covalentlybonded perimeters 42 may be advantageous in certain situations when thearticle 2 (thin sheet 20 together with carrier 10) is diced for furtherprocessing of devices on smaller sections, as desired.

Second Embodiment of the Third Use

According to another embodiment, a pattern of covalent bonding areas 40and controlled bonding areas 50 may be formed by patterning the surfacemodification layer 30 prior to connecting the thin sheet 20 with thecarrier 10 via the surface modification layer. Either additive orsubtractive methods may be used.

For example, the surface modification layer 30 may be deposited onto thecarrier 10 in a patterned manner so as to only be within the controlledbonding areas 50 as shown in FIG. 6 or 11. In order to deposit thesurface modification layer 30 in a pattern, a mask may be used to coverthe areas of the carrier bonding surface that are to form covalentbonding in areas 40. The non-masked areas then correspond to areas 50 inwhich there will be controlled bonding due to deposition of the surfacemodification layer 30 there. Other additive methods of patterning thecontrolled bonding area, by depositing material to form the controlledbonding area, include printing, shadow masking in vapor deposition, orinkjet printing, for example. The materials and surface treatmentsaccording to examples 2a (in situations where there will be noultrasonic processing during device fabrication), 2c, 2d, 2e, 3a, 3b,4b, 4c, 4d, and 4e, may be deposited on the carrier 10 to produce thedesired degree of controlled bonding in areas 50.

Alternatively, the controlled bonding within areas 50 may be produced bysubtractive methods. That is, the entire surface of the carrier 10 maybe provided with a surface modification layer 30, and then portions ofthat surface modification layer 30 may then be removed to form exposedareas on the bonding surface of the carrier. For example, the surfacemodification layer 30 may be ablated with a laser. The exposed portionson the carrier bonding surface may then be used to covalently bond withcorresponding portions of the thin sheet 20 disposed in an adjoiningmanner therewith. Other methods of subtractive patterning may be used,for example, photolithography and plasma etch, UV, corona discharge, oratmospheric plasma torch.

Once the surface modification layer 30 is formed within the desiredconfiguration of controlled bonding areas 50 on the carrier 10, the thinsheet 20 is then connected to the carrier via the surface modificationlayer 30.

Subsequently, the article is heated to an appropriate degree to providethe desired covalent bonding in areas 40 where there is no surfacemodification layer 30 present between adjoining portions of the bondingsurfaces of the carrier 10 and thin sheet 20. After the desired covalentbonding is formed in areas 40, the desired parts 56 may be formed on thethin sheet 20, and removed from the carrier 10 in the same manner asdescribed above in connection with the first embodiment.

Although the surface modification layer 30 was described above as beingformed on the carrier 10, it could instead be formed on the thin sheet20. In certain situations, a surface modification layer may be used onboth the thin sheet and the carrier; in such situations, as when usingthe material and associated surface treatment of example 2a, forexample, corresponding patterns are made on each the carrier and thinsheet. The patterns may be made using the same techniques, or differenttechniques.

CONCLUSION

It should be emphasized that the above-described embodiments of thepresent invention, particularly any “preferred” embodiments, are merelypossible examples of implementations, merely set forth for a clearunderstanding of various principles of the invention. Many variationsand modifications may be made to the above-described embodiments of theinvention without departing substantially from the spirit and variousprinciples of the invention. All such modifications and variations areintended to be included herein within the scope of this disclosure andthe present invention and protected by the following claims.

For example, although the surface modification layer 30 of manyembodiments is shown and discussed as being formed on the carrier 10, itmay instead, or in addition, be formed on the thin sheet 20. That is,the materials as set forth in the examples 4 and 3 may be applied to thecarrier 10, to the thin sheet 20, or to both the carrier 10 and thinsheet 20 on faces that will be bonded together.

Further, although some surface modification layers 30 were described ascontrolling bonding strength so as to allow the thin sheet 20 to beremoved from the carrier 10 even after processing the article 2 attemperatures of 400° C., or of 600° C., of course it is possible toprocess the article 2 at lower temperatures than those of the specifictest the article passed and still achieve the same ability to remove thethin sheet 20 from the carrier 10 without damaging either the thin sheet20 or the carrier 10.

Still further, although the controlled bonding concepts have beendescribed herein as being used with a carrier and a thin sheet, incertain circumstances they are applicable to controlling bonding betweenthicker sheets of glass, ceramic, or glass ceramic, wherein it may bedesired to detach the sheets (or portions of them) from each other.

Further yet, although the controlled bonding concepts herein have beendescribed as being useful with glass carriers and glass thin sheets, thecarrier may be made of other materials, for example, ceramic, glassceramic, or metal. Similarly, the sheet controllably bonded to thecarrier may be made of other materials, for example, ceramic or glassceramic.

Still further yet, the article may be cleaned, using appropriate ones ofthe above-described cleaning methods, or others known in the art, afterremoving the surface modification, and prior to heating to form apermanent covalent bond. After the cleaning, the exposed portions of thethin sheet and carrier should be sufficiently dried to facilitateforming the subsequent covalent bond between the thin sheet and thecarrier.

It is to be understood that various features disclosed in thisspecification and in the drawings can be used in any and allcombinations. By way of non-limiting example the various features may becombined with one another as set forth in the following aspects:

According to a first aspect, there is provided a method of forming anarticle, comprising:

obtaining a glass sheet having a glass-sheet bonding surface;

obtaining a glass carrier having a carrier bonding surface;

coating at least one of the glass sheet and carrier bonding surfaceswith a surface modification layer;

connecting the glass sheet with the carrier via the surface modificationlayer;

removing, from the perimeter of the glass sheet and the carrier whileconnected, a portion of the surface modification layer so as to expose aportion of the bonding surface on each of the glass sheet and thecarrier, wherein the exposed portion of the glass-sheet bonding surfaceadjoins the exposed portion of the carrier bonding surface; and

heating, after the removing and the exposing, the glass sheet andcarrier at a temperature ≧400° C. but less than the strain point of boththe glass of the glass sheet and the glass of the carrier so as to bondthe perimeter of the glass sheet bonding surface with the perimeter ofthe carrier bonding surface.

According to a second aspect, there is provided the method of aspect 1,wherein the glass-sheet bonding surface has an area equal to that of thecarrier bonding surface.

According to a third aspect, there is provided the method of aspect 1 oraspect 2, wherein the removing comprises, in a vacuum chamber, treatingthe thin sheet as connected to the carrier with an O2 plasma.

According to a fourth aspect, there is provided the method of aspect 1or aspect 2, wherein the removing comprises using UV radiation, heat,ablation of the surface modification layer with laser energy, orcombinations thereof.

According to a fifth aspect, there is provided the method of any one ofaspects 1-4, further comprising cleaning at least the exposed portionsof the glass sheet and the carrier after the step of removing and priorto the step of heating.

According to a sixth aspect, there is provided the method of aspect 5,further comprising drying at least the exposed portions of the glasssheet after the cleaning and prior to the heating.

According to a seventh aspect, there is provided the method of any oneof aspects 1 to 6, wherein prior to coating, the at least one of thethin-sheet bonding surface and the carrier bonding surface is cleanedwith one or more of the following: UV-Ozone, O2 plasma, DI-O3 water,SC1, SC2, wash chemistry including HF, or wash chemistry includingH2SO4.

According to an eighth aspect, there is provided the method of any oneof aspects 1 to 7, wherein the surface modification layer comprises analkyl silane, a fluoro alkyl silane, an aromatic silane, a fluoro orchloro aromatic silane, or HMDS.

According to a ninth aspect, there is provided the method of any one ofaspects 1 to 8, wherein both of the thin-sheet and carrier bondingsurfaces are coated with a surface modification layer.

According to a tenth aspect, there is provided the method of any one ofaspects 1 to 8, wherein only one of the thin-sheet and carrier bondingsurfaces is coated with a surface modification layer, and the other oneof the thin-sheet and carrier bonding surfaces is heat treated so as toreduce the hydroxyl concentration thereon to a level substantially thesame as if that surface was SC1 cleaned and then heated at 450° C. for 1hour.

According to an eleventh aspect, there is provided the method of any oneof aspects 1 to 10, wherein the connecting comprises forming van derWaals bonding between the thin sheet, the carrier, and the surfacemodification layer.

According to a twelfth aspect, there is provided the method of any oneof aspects 1 to 11, wherein the surface modification layer is 0.1 to 100nm thick.

According to a thirteenth aspect, there is provided the method of anyone of aspects 1 to 11, wherein the surface modification layer is 0.1 to10 nm thick.

According to a fourteenth aspect, there is provided the method of anyone of aspects 1 to 11, wherein the surface modification layer is 0.1 to2 nm thick.

According to a fifteenth aspect, there is provided the method of any oneof aspects 1 to 11, wherein the surface modification layer is aself-assembled monolayer.

According to a sixteenth aspect, there is provided the method of any oneof aspects 1 to 15, wherein the glass sheet has a thickness of ≦300microns.

According to a seventeenth aspect, there is provided the method of anyone of aspects 1 to 16, wherein the carrier has a thickness of 200microns to 3 mm.

According to an eighteenth aspect, there is provided an article producedby the simplified processing, specifically, there is provided a glassarticle comprising:

a glass sheet having a glass-sheet bonding surface;

a glass carrier having a carrier bonding surface;

a surface modification layer disposed on at least one of the glass-sheetbonding surface and the carrier bonding surface;

wherein the glass sheet and carrier are connected via the surfacemodification layer,

wherein a perimeter of the glass-sheet bonding surface is affixed to thecarrier, whereby the glass sheet and carrier act as a monolith at theaffixed perimeter.

According to a nineteenth aspect, there is provided the glass article ofaspect 18, wherein a perimeter of the carrier bonding surface remainsuncoated by the surface modification layer, wherein a perimeter of theglass-sheet bonding surface remains uncoated by the surface modificationlayer, and wherein the uncoated perimeter of the carrier bonding surfaceis affixed to the uncoated perimeter of the glass-sheet bonding surface.

According to a twentieth aspect, there is provided the glass article ofaspect 18 or aspect 19, wherein the surface modification layer comprisesan alkyl silane, a fluoro alkyl silane, an aromatic silane, or a fluoroor chloro aromatic silane.

According to a twenty first aspect, there is provided the article ofaspect 18 or aspect 19, wherein the surface modification layer comprisesHMDS.

According to a twenty second aspect, there is provided the article ofany one of aspects 18 to 21, wherein the surface modification layer is0.1 to 100.0 nm thick.

According to a twenty third aspect, there is provided the method of anyone of aspects 18 to 21, wherein the surface modification layer is 0.1to 10.0 nm thick.

According to a twenty fourth aspect, there is provided the method of anyone of aspects 18 to 21, wherein the surface modification layer is 0.1to 2.0 nm thick.

According to a twenty fifth aspect, there is provided the method of anyone of aspects 18 to 21, wherein the surface modification layer is aself-assembled monolayer.

According to a twenty sixth aspect, there is provided the article of anyone of aspects 18 to 25, wherein a surface modification layer isdisposed on each of the glass sheet and carrier, and further wherein thematerial of the glass-sheet surface modification layer is the same asthat of the carrier surface modification layer.

According to a twenty seventh aspect, there is provided the article ofany one of aspects 18 to 26, wherein the glass sheet has a thickness of≦300 microns.

According to a twenty eighth aspect, there is provided the article ofany one of aspects 18 to 27, wherein the carrier has a thickness of 200microns to 3 mm.

What is claimed is:
 1. A method of forming an article, comprising:obtaining a glass sheet having a glass-sheet bonding surface with aperimeter; obtaining a glass carrier having a carrier bonding surfacewith a perimeter; coating at least one of the glass sheet and carrierbonding surfaces with a surface modification layer; connecting the glasssheet with the carrier via the surface modification layer; removing,from the perimeter of the glass sheet and the carrier while connected, aportion of the surface modification layer so as to expose a portion ofthe bonding surface on each of the glass sheet and the carrier, whereinthe exposed portion of the glass-sheet bonding surface adjoins theexposed portion of the carrier bonding surface; and heating, after theremoving and the exposing, the glass sheet and carrier at a temperature≧400° C. but less than the strain point of both the glass of the glasssheet and the glass of the carrier so as to bond the perimeter of theglass sheet bonding surface with the perimeter of the carrier bondingsurface.
 2. The method of claim 1, wherein the glass-sheet bondingsurface has an area equal to that of the carrier bonding surface.
 3. Themethod of claim 1, wherein the removing comprises, in a vacuum chamber,treating the glass sheet as connected to the carrier with an O2 plasma.4. The method of claim 1, wherein the removing comprises using UVradiation, heat, ablation of the surface modification layer with laserenergy, or combinations thereof.
 5. The method of claim 1, wherein priorto coating, the at least one of the glass-sheet bonding surface and thecarrier bonding surface is cleaned with one or more of the following:UV-Ozone, Oxygen plasma, ozonated deionized water (DI-O₃), standardclean 1 (SC1), standard clean 2 (SC2), wash chemistry including hydrogenfluoride (HF), or wash chemistry including sulfuric acid (H₂SO₄).
 6. Themethod of claim 1, wherein the surface modification layer comprises analkyl silane, a fluoro alkyl silane, an aromatic silane, a fluoro orchloro aromatic silane, or hexamethyldisilazane (HMDS).
 7. The method ofclaim 1, wherein both of the glass-sheet and carrier bonding surfacesare coated with a surface modification layer.
 8. The method of claim 1,wherein only one of the glass-sheet and carrier bonding surfaces iscoated with a surface modification layer, and the other one of theglass-sheet and carrier bonding surfaces is heat treated so as to reducethe hydroxyl concentration thereon to a level substantially equal to ahydroxyl concentration on a glass surface that was cleaned with astandard clean 1 and then heated at 450° C. for 1 hour.
 9. The method ofclaim 1, wherein the surface modification layer is 0.1 to 100 nm thick.10. The method of claim 1, wherein the surface modification layer is aself-assembled monolayer.
 11. The method of claim 1, wherein the glasssheet has a thickness of ≦300 microns.
 12. The method of claim 1,wherein the carrier has a thickness of 200 microns to 3 mm.